Potentiometer



J. F. SHEA POTENTIOMETER March 27, 1962 Filed May 25, 1959 pm. T. L g5w. 6 f. d M a w J J/f 1` a m "J mmlm;

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Unite ttes Filed May 25, 1959, Ser. No. 815,721 9 Claims. (Cl. SSS-130)This invention relates to rotary potentiometers and more particularlyrotaryl potentiometers specially adapted for construction andutilization in miniature and subminiature sizes.

The herein invention provides a novel design and configuration for thistype of potentiometer making possible the construction of an extremelycompact device such that a potentiometer can be built havingapproximately one-half the size of heretofore known potentiometershaving similar or superior ranges of performance.

Theinvention features a unique design wherein the potentiometer housingis formed in two sections enclosing terminals and providing aconfiguration having within it a toroidal or doughnu-t-like cavity inwhich are mounted one or more adjustable circular resistance elements, acircular preferably wafer thin contactor member n vdual turns ormultiple turns in a type of device utilizing a resistance member in theform of a flat helix or spiral.

The particular configuration of the invention has the further object andprovides the additional advantage of facilitating the gauging of aplurality of the potentiometers on a common shaft in such a manner as toprovide a very compact ganged assembly and one which is particularlyshort in axial length and being an improvement over prior art devices inthis respect.

- In addition to the foregoing stated objectives and advantages of theinvention, it has the further objective of improving the operating andperformance characteristics of the devices by providing humidity sealingindividually and between ganged sections and at points of lattachment ofterminals.

Another object is to improve the antivibration characteristics of apotentiometer by providing a configuration as set out in the foregoing,wherein molded in wiper contactors or brushes are sandwiched in thetoroidal cavity between a resistance member and a contactor member andfurther by providing plural iexible lingers engaging each of theelements.

Anotheriobject is to provide a potentiometer configuration which isrotative for phasing when a group of potentiometers are ganged withoutbreaking humidity seals between units.

Another objective is to provide a configuration as set out in theforegoing specially adapted to provide for and make possible theutilization of dual composition or multiple turn resistance units inhousings of the same size as normally utilized for single turn un-ts.

-Another object is to provide a potentiometer configuration as set outin the foregoing, wherein a wire or other resistance element having asingle turn for example, and a resistance up to 200K ohms may beassembled in a housing of approximately inch diameter.

Another object is to provide a potentiometer as in the foregoing havinga radial stem carrying the wiper contacts or brushes and improved meansfor accurately guiding the rotative movement comprising a generallyspherical ball on the stern moving in a toroidal guide channel in thehousing. t

Another object is to provide a potentiometer design operable attemperatures of approximately 200 C.

Further objects and numerous additional advantages of atent theinvention will become apparent from the following detailed descriptionand annexed drawings wherein:

In the drawings:

FIG. l is a sectional view of a preferred form of the invention showingpotentiometers ganged on a shaft;

FIG. 2 is an end view of the structure of FIG. l;

FIG. 3 is a detail view of one of the circular contact members and itsconnection to a terminal;

FIG. 4 is a detail view of another of the contactor members and itsconnection to its respective terminal member; and

FIG. 5 is a detail View of the connection of the terminal members to thecircular resistance element.

FIG. l of the drawings shows in section a group of three of thepotentiometers segmented together on a common shaft. Each 'of thepotentiometer units individually is formed in sections. Depending uponthe operating temperature to which the units are to be subjected, theymay be made of different materials. For example, for higher temperaturesthe sections and certain other parts may be made of stainless steel andthe insulative parts of molded Teflon. For lower temperature unitsoperating at, for example, up to C., the housing sections may be made ofanodized aluminum material or the sections or segments may be molded ofcommercial grade phenolic, that is, plastic material.

In FIG. 1 of the drawings, the three ganged potentiometers aredesignated generally by the numerals 10, 11 and 12. The rstpotentiometer to the right designated by the numeral 10, is formed oftwo mating sections as designated at 14 and 15 having the shape andconfiguration as shown in cross-section in this figure. The section 15has an extending boss or threaded f1tting 17 and/or servo mountingadapted for mounting the unit and the two sections have central bores asshown, for coaxially mounting them on an operating Shaft 1S. Section 14may have molded in place bracket 9 for virtually any mounting situation.Unit 12 may have a corresponding bracket.

The sections 15 and 14 have facing annular arcuate depressions asindicated at 20 and 21 respectively; the two sections tit together andthe depressions 20 and 21 are of a size to form a toroidal cavity withinthe housing formed by the sections, or the cavity may be consideredsubstantially doughnut-shaped. The central parts of the sections 14 and15 are spaced apart as shown, and the sections have additional annulargrooves or depressions which are arcuate in cross-section as indicatedat 23 in section 15 and at 24 in section 14. These depressions asbetween the two sections form a second toroidal cavity in the housinghaving a purpose which will be referred to presently.

The outer edges of the sections 14 and 15 lit together and at angularlyspaced points the outer edges of each section have arcuate cavities ordepressions so that when the sections fit together, radial openings areprovided as indicated, for example, at 26 to receive the mountings ofthe electrical terminals. Three radial openings such as 26 are providedat the top and botto-m of the potentiometer unit or on opposite sides,as may be seen in FIG. 2 of the drawings.

The section 15 has a counter bore 27 on the inside thereof and fittingin this counterbore is a sealing member 23 having a U-shaped crosssection as shown. The sealing ring 28 is of a known commercial type madeof a material suitably adapted to humidity seal the unit-as rcspects theshaft 18. Alternatively a miniature ball bearing may be provided incounter bore 27 or both the ball bearing and the sealing ring may beprovided. Section 14 has cavity 29 and sealing O-ring 30 which bearsagainst stem 40. Cavity 27 may have a similar O-ring with the ringsfrictionally engaging stem 4) to provide for example, tive inch-ouncesof drag between the shaft and stem.

j, helical winding of wire on a base iform or adjustable mandrel which,in this instance, is ring-shaped, that is, toroldal-shaped.,l Preferablyin fabricating these ringshaped resistance members, this is accomplishedby splitting a helical unit lengthwise along one side and thenV joiningVthe ends of individual convolutions to form a ring. Helical windingsadjacent the joint are stripped away to provide for the terminalconnectionsto the ends of the resistor element lthus formed. A unit thusformed vis shown in FIG. 5.

The adjustable resistance elements or units 32 and 33 "are preferablycemented into the section 14 against a side wall of the toroidal cavityas shown. FIG. shows by vWay of example one of the resistance elementsand the connections of the Iterminals thereto which will be referred toagain presently.

'Within rthe toroidal cavity opposite the resistance elements,that isspaced axially therefrom, on the inside of theopposite wall of thecavity, are disposed preferably wafer thin, eg. approximately .003 inchthick, ring-shaped contacter members as dsignated at 35 and 36. The two'contactor members are spaced from each other and insulated from eachother as may be seen. The configuration yof these contactor members isshown in detail in IFIGS. 3 and 4. These members are cemented againstthe internal side wall of Ithe toroidal cavity, that is, against lthesection 15. With reference to .the `electrical elements .1n the toroidalcavities, other types may be employed and of other materials such ascarbon'or graphite.

The device bein-g described provides for a dual output, that is, thereare two circular resistor elements with their cooperating circularcontact members and three `terminals are provided as will be described,associated with each l'of the dual outputs.

` elements V32, and 33 and their respective contactors or l'contactingmembers 35 and 36. Oppositely disposed brushes or wipers are provided indiametrically opposed positions since, as stated, the unit is of thedual output type. In FIG. 1 numeral 40 designates a tube extending'transversely through an aperture in the shaft 18 and in the spaceprovided between the central portions ofthe sections 14 and 15. Numeral41 designates a fabricated block of insulating material, preferablyTeflon, having a cylindrical stern 42 which is self-threading andadjustable, which is threaded into the internally threaded end of thetube 40 to hold the wipers or brushes in position. The wipers or brushesthemselves are in the form of a plurality of flexible contacting ngers43 which have por- 'tions extendin-g through openings in `the block 4Iand yangular portions as shown which on one side engage the resistanceelements 32 and 33 and on the other side engage thercircular contactmembers 35 and 36. The material of the wiper fingers themselves may be amaterial known commercially as Palinay wire. These flexible fingers, asmay be seen, bridge the resistance element 32 to the circular contactor35- and the resistance element 33 to the con- Y tactor element 36.`Wiper fingers 43 may be molded into block 41.

annular Vgrooves or depressions 23 and 24 formed in the sectionsvlS' and14 `which are of a size that Iball 46 engages the surface 24. The member46 is of precision construction and rolls on its shaft for accurate andprecise positioning and guidance of the Fwipercontacts in the toroidalcavity and prevents back-lash. Member 46 and a similarV member inpotentiometer 12 axially position the shaft 18,.

as may be observed from the drawings.

The construction of the brushes or wipercontacts at the opposite end ofthe tube 40 is identical and will not therefore be described in detail.The guide rnechanismvincluding the spherical member 47 at the oppositeend of the .tube 40'is also the same. The'constructionas just describedcontributes to precision and` vhigh resolution in the potentiometer unitand to its' improved vanti-vibration and anti-back-lash characteristics.Y

The three upper terminals of `the potentiometer unit are designatedl atS0, 51 and 52 in FIG. 2,-and the three lower terminals are designed at53, 54 and 55. As shown, these terminals are of a turret type made ofasuitable conducting material. Each of these terminals fits within ahanged insulative bushing as shown by way of example at 60 for theterminal 54 Vin FIG. 1. 26, as previously described,V is fitted with oneofthe hanged bushings 60. yThe bushing 60 has anrinternal ange as shownat 61 which engages within the toroidal cavity as shown in FIG. 1, andan external flange 62 which lits against the outside of the `housing asshown. As may be seen in FIG. 3, a contact'strip or strap 64 connects toan edge of the contact member35 and leads up into the bushing 60 and hasan end portion or tab-65 which engages the end of the terminal as shownand is held thereagainst by suitable means. The connection to thecontactor member 36 is similar, there being a longer contact strip orstrap 63 extending up into the bushing and being similarly held againstthe end of the terminal member. The connections to all of the externalterminals connected to circular contact strips in the unit are the same.The terminals may be of molded-in-place construction.

FIG. 5 shows the manner of connecting the terminals to the ends of thecircular resistance elements, `for exam'- ple, the element 32, as shownin FIG. 5. The terminals are shown in this figure by way of example asbeing terminals 51 and 52 connected as by means of conducting elements71 and 72 to the ends ofjthe winding forming the resistance element 32,this latter element having a central core, or mandrel, as shown at 73.

The section 1K4 of the potentiometer'unit lil `has a central circulardepression or inset as shown at 76 the purpose of which is to providefor intertting engagement with another potentiometer unit when the unitsare ganged on a common shaft, the gauging being accomplished 1in a wayresulting in a'minimum axial llength of the assembled unit.

The potentiometer units 11 and 12 'are the same as vthe unit 10 whichhas been described in detail except for specific features which inthemselves will be ydescribed hereinafter. Optionally the shafts ofunits may bekeyed together by male and female joints as shown at 81lthus segmenting the units adapting them especially as trimmers.

Section 15 of the unit 11 has a circular boss or raised portion 77 whichfits into the depression `or inset 76 in the unit 10 when the units areganged and the units are cemented together vat this joint Vin a mannerto provide for humidity sealing. Also, Vthere is vin theboss 77 anannular groove or depression 78 which fitsg'a sealing O-ring 79 of a1material adapted for providing humidity sealing between sections. y Theunit 11 has provided a 'hub 84 which may be secured on the shaft 18 byway of pressed in ipins 484. Fl`he hub 84 has Oppositely disposed radialopenings or vchannels and these channels are adapted to'rec'eive tubesas shown at S5 and 86 which form legs carrying the Contact brushes orwipers, as described -in connection withk potentiometer 10. Phasing asbetween units \may `be Each of the holes f accomplished by circularlyadjusting the position of the hub 84 on the shaft 18.

The potentiometer unit 1.2 is like 11 except that its section 14 has acentral cylindrical cavity 89 having mounted in it a ball bearingincluding a bushing as shown at 90, and a ring member 91 forming a ballrace for the ball bearings as shown. The end of theshaft 18 is receivedin the ball bearing which is a subminiature type wherein precision balls91' ride in place to prevent backlash. 'l

In operation the unit 10 may be mounted by way of the screw threadednipple or boss 17 and/ or servo-mount. The shaft 18 is rotated inresponse to any appropriate input and corresponding voltages are takenoff from the terminals 50 to 55 with reference to the unit 10. Theoutput is dual, as explained, the separate outputs being by way of theterminals at the top and bottom, as seen in FIG. 2.

When ganged, the potentiometers are sealed together as described and theoutputs are taken off in a corresponding manner. The units are rotativefor phasing when ganged without breaking the humidity seals.

The units may provide one turn or dual turns or multiple turns, whichwould be by way of a fiat helical resistance element, or compositionsubstantially filling the cavity 21. The device has the advantage thatthe same size housing may be utilized for a single turn or dual turn ormultiple turn element. Units having an unusually wide resistance rangecan be made in smaller sizes and particularly with a shorter axiallength. In addition to the advantages previously set forth, it has beenfound that potentiometers constructed in accordance with this inventionhave shown improvement in noise level characteristics, life ofinstrument, torque, moment of inertia, linearity, and in other respectsdue to simplification and compactness of the design.

The foregoing disclosure is illustrative of a preferred form of theinvention and is to be interpreted in an illustrative rather-'than alimiting sense. Various modifications and alternatives may occur to andbe adopted by those skilled in the art without departing from the spiritand scope of the invention, which is to be in accordance with the claimsappended hereto.

What is claimed is:

l. In a potentiometer, in combination: a resistance element of circularform, a circular contact member spaced axially from the resistanceelement, housing means having a central shaft enclosing said resistanceelement and contact member, rotatable contacting means disposed betweenthe resistance element and the contact member and engageable with them,said shaft having a rigid radial stern carrying said rotatable contactmeans, the said housing means having a configuration to form an internalcavity of toroidal shape having the resistance element and circularcontacting member disposed in said cavity and the contacting memberbeing arcuate in cross-section adapting it to fit against the interiorof the toroidal cavity.

2. In a potentiometer, in combination: a plurality of resistanceelements of circular form, a plurality of circular contact membersspaced axially from the resistance elements, housing means having acentral shaft enclosing said resistance elements and contact members androtatable contacting means disposed between the resistance elements andthe contact members and engageable with them, said shaft having a rigidradial stem carrying said rotatable contact means and said housinghaving aconiiguration to form an internal cavity of toroidal shapehaving the resistance elements and circular contacting members disposedin said cavity.

3. In a potentiometer, in combination: a resistance element of circularform, a circular contact member spaced axially from the resistanceelement, housing means having a central shaft enclosing said resistanceelement and contact member, rotatable contacting means disposed betweenthe resistance element and the contact member and engageable with them,said shaft having a rigid radial stem carrying said rotatable contactmeans, the housing means having a configuration to form an internalcavity of toroidal shape having the resistance element and circularcontacting member disposed in the cavity, and the housing being formedby two generally circular sections each having a cavity portion formedin it.

4. A potentiometer as in claim 3, including a second similarpotentiometer adapted to be ganged therewith on a common axial shaft,said two potentiometers having adjacent sections having configurationsadapting them to closely interft together.

5. A structure as in claim 4, including humidity sealing meansinterposed between the two interftting sections of the potentiometers.

6. A potentiometer housing comprising generally cir-l cular matingsections having a configuration to form a structure having atoroidal-shaped cavity within it, circular resistance means and acircular contact member within the cavity spaced axially from eachother, rotatable electrical contacting means positioned between theresistance member and the contact member, an axial shaft having a radialstem for rotating the contacting means, said sections having a spacebetween their central portions to accommodate said stem, rotatablecontacting means including a guide member disposed on the radial stem,and said housing sections having oppositely disposed annular groovesforming a circular channel in which said guiding member moves.

7. A potentiometer as in claim 6, wherein said channel is toroidal andsaid guide member is generally spherical having engagement with one sideof said channel.

8. A potentiometer housing comprising generally circular mating sectionshaving a configuration to form a structure having a toroidal-shapedcavity within it, circular resistance means and a circular contactmember within the cavity spaced axially from each other, rotatableelectrical contacting means positioned between the resistance member andthe contactor member, an axial shaft having a radial stem for rotatingthe contacting means, said sections having a space between their centralportions to accommodate said stern, a second similar potentiometeradapted to be ganged with said first potentiometer and mounted on acommon shaft, said two potentiometers having adjacent housing sectionshaving a configuration to interft each other forming a ganged structureof relatively short axial length, and humidity sealing means' interposedbetween the two potentiometers around the coaxial shaft.

9. A potentiometer structure as in claim 8, including two circularresistance elements of different adjustable diameters within the cavityin the housing and two circular adjustable contact members of differentdiameters within the housing, and a plurality of radially extendingterminals extending radially from the cavity within the housing, saidterminals being in two sets diametrically opposed on the housing, oneset having connections with one potentiometer formed by a resistanceelement and a contacting member, and the other having electricalconnection with a second potentiometer formed by a resistance elementand a contacting member.

References Cited in the file of this patent UNITED STATES PATENTS2,551,989 Wilson May 8, 1951 2,595,189 Dewan Apr. 29, 1952 2,798,926Mucher July 9, 1957 2,881,295 Brown Apr. 7, 1959 2,898,567 Drewitz etal. Aug. 4, 1959

